Schnitzer E, Pinchuk I, Bor A, Fainaru M, Lichtenberg D
Department of Physiology and Pharmacology, Tel-Aviv University, Sackler School of Medicine, Ramat Aviv, Israel.
Biochim Biophys Acta. 1997 Feb 18;1344(3):300-11. doi: 10.1016/s0005-2760(96)00154-3.
In an attempt to gain deeper understanding of the mechanism or mechanisms responsible for the protective effect of serum albumin against Cu(2+)-induced peroxidation of low density lipoprotein (LDL), we have examined the influence of the concentrations of bovine serum albumin (BSA), Cu2+ and LDL on the kinetics of peroxidation. Since the common method of monitoring the oxidation by continuous recording of the absorbance of conjugated dienes at 234 nm cannot be used at high BSA-concentrations because of the intensive absorption of BSA, we have monitored the time-dependent increase of absorbance at 245 nm. At this wavelength, conjugated dienes absorb intensely, whereas the background absorbance of BSA is low. Using this method, as well as the TBARS assay for determination of malondialdehyde, over a large range of BSA concentrations, we show that in many cases the influence of BSA on the kinetics of oxidation can be compensated for by increasing the concentration of copper. This reconciles the apparent contradiction between previously published data. Detailed studies of the kinetic profiles obtained under different conditions indicate that binding of Cu2+ to albumin plays the major role in its protective effect while other mechanisms contribute much less than copper binding. This conclusion is consistent with the less pronounced effect of BSA on the oxidation induced by the free radical generator AAPH. It is also shown that the copper-albumin complex is capable of inducing LDL oxidation, although the kinetics of the latter process is very different from that of copper-induced oxidation. Nevertheless, when compared to copper induced oxidation at similar concentration of the oxidation-promotor, the kinetics of oxidation induced by copper-albumin complex is very different and is consistent with a tocopherol mediated peroxidation, characteristic under low radical flux. Similar kinetics was observed for copper-induced oxidation only at much lower copper concentrations.
为了更深入地了解血清白蛋白对铜（Ⅱ）诱导的低密度脂蛋白（LDL）过氧化具有保护作用的一种或多种机制，我们研究了牛血清白蛋白（BSA）、铜离子（Cu2+）和LDL的浓度对过氧化动力学的影响。由于在高BSA浓度下，无法使用通过连续记录234nm处共轭二烯吸光度来监测氧化的常用方法，因为BSA的吸收很强，所以我们监测了245nm处吸光度随时间的增加。在这个波长下，共轭二烯强烈吸收，而BSA的背景吸光度较低。使用这种方法以及用于测定丙二醛的TBARS测定法，在很大范围的BSA浓度下，我们表明在许多情况下，BSA对氧化动力学的影响可以通过增加铜的浓度来补偿。这调和了先前发表的数据之间明显的矛盾。对在不同条件下获得的动力学曲线的详细研究表明，Cu2+与白蛋白的结合在其保护作用中起主要作用，而其他机制的贡献远小于铜结合。这一结论与BSA对自由基引发剂AAPH诱导的氧化作用不太明显的效果一致。还表明铜 - 白蛋白复合物能够诱导LDL氧化，尽管后一过程的动力学与铜诱导的氧化动力学非常不同。然而，与在相似氧化促进剂浓度下铜诱导的氧化相比，铜 - 白蛋白复合物诱导的氧化动力学非常不同，并且与生育酚介导的过氧化一致，这是低自由基通量下的特征。仅在低得多的铜浓度下，铜诱导的氧化才观察到类似的动力学。
